Data over cable service interface specification (DOCSIS) is an international telecommunications standard that permits the addition of high-speed data transfer to an existing cable television system. To maintain cross-version compatibility across all versions of DOCSIS, cable television operators utilize cable modems that support DOCSIS 1.X, 2.X, and 3.0, and that fall back to the highest supported version in common between both endpoints. Cable television operators use DOCSIS 3.0 to provide two-way communication over their existing hybrid fiber-coaxial (HFC) infrastructure.
An HFC network is a broadband network that combines optical fiber and coaxial cable. The HFC network is a two-way communication network between a cable modem termination system (CMTS) and a cable modem. The CMTS is communication equipment typically located in a cable operator's headend facility. The CMTS collects and processes communication signals, distributes those signals to customer locations using downstream channels, and receives other communication signals from the customer locations on upstream channels. The cable modem is a communication device that receives the communication signals on the downstream channels from the CMTS, and transmits the other communication signals to the CMTS on the upstream channels. The cable modem may be a standalone device that connects to the Internet, or integrated with a set-top box.
The DOCSIS 1X and 2.X specifications describe the channel frequency and modulation characteristics for downstream and upstream transmissions. When the CMTS communicates with a device, the DOCSIS 1.X or 2.X cable modem at a customer location uses the frequencies (channels) of the CMTS transmitter and receiver to which the modem is physically connected to carry the downstream and upstream transmissions. The term “channel” as used herein is synonymous with the term “receiver”. If the channel becomes impaired, the modulation mode of the channel can drop, resulting in a reduction in the bandwidth to the device.
Channel bonding is a DOCSIS 3.0 feature that enables a DOCSIS 3.0 cable modem at a customer location to use multiple downstream channels, or multiple upstream channels, together at the same time. For example, a cable modem configured with four upstream channels can use DOCSIS 3.0 channel bonding to increase the throughput of the upstream communication with the CMTS. The cable modem distributes, or segments, the data packets among the four channels in an upstream bonding group and transmits the data packets to the CMTS in parallel, rather than in series. When the upstream bonding group operates in full service mode, the CMTS receives and reassembles the data packets on all four channels in the upstream bonding group. If there is a problem receiving data packets on a CMTS receiver, due to an upstream channel that is associated with the receiver being impaired or unavailable, the CMTS cannot properly reassemble the data packets for the upstream bonding group and data loss or throughput degradation will result. The detection of this problem will allow communication to continue between the CMTS and cable modem by transitioning the upstream bonding group to operate in partial service mode by disabling data grant scheduling on the faulty receiver/channel.
When DOCSIS 1.X, 2.X, and 3.0 modems are registered to use a channel that becomes impaired, a decrease in bandwidth on the impaired channel, which can also result from a lowering of the modulation profile due to noise, is a greater impact on the DOCSIS 1.X and 2.X modems, because the DOCSIS 3.0 modem has other bonded channels to use for data passing as long as the impaired channel is in partial service mode. If the DOCSIS 3.0 modem is not yet in partial service mode, the DOCSIS 3.0 modem cannot reassemble the packets. In addition, the reduction in bandwidth may cause an increase in utilization based on the bandwidth size, and may trigger unnecessary load balancing with the possibility of losing modems when they attempt to move to another channel. Furthermore, a configuration change by the cable operator may cause a decrease in the modulation mode. There is a need for a method of controlling when a channel transitions to partial service mode to make valuable bandwidth available for other resources. The presently disclosed invention satisfies this demand.